Field of the Invention
The present invention relates to a gas-liquid separator for separating a gas-liquid two-phase flow, which is generated from an apparatus that uses a liquid, especially a liquid (foamable liquid) which is likely to generate bubbles, into a gas and a liquid and discharging them, and further relates to a polishing apparatus provided with such a gas-liquid separator.
Description of the Related Art
A polishing apparatus is known as a device for polishing a substrate surface while supplying a polishing liquid (slurry) onto a polishing surface. In the polishing apparatus, a gas-liquid two-phase flow is generated which is composed of a polishing liquid, containing a polishing agent and abrasive grains, and a gas, such as nitrogen gas, which is supplied during polishing or cleaning. Such a gas-liquid two-phase flow can also be generated when the gas, such as nitrogen gas, is mixed with the waste of a cleaning liquid after its use in cleaning of the polishing surface, or when a gas is mixed into the polishing liquid or the waste cleaning liquid.
In order to prevent such a gas-liquid two-phase flow from flowing into an exhaust line and causing clogging of the exhaust line with a liquid, a polishing apparatus is generally provided with a gas-liquid separator for separating a gas-liquid two-phase flow into a gas and a liquid and separately discharging them.
FIG. 1 is a vertical cross-sectional front view of an exemplary conventional gas-liquid separator. As shown in FIG. 1, the gas-liquid separator includes a cylindrical gas-liquid separation tank 100 with an open top and a closed bottom, and a gas-liquid introduction pipe 104 for introducing a gas-liquid two-phase flow, which has been generated e.g., on a polishing table (not shown) and recovered in a drain receiver 102, into the gas-liquid separation tank 100. A vertical connecting pipe 106 is coupled to a bottom of the drain receiver 102. The gas-liquid introduction pipe 104 is coupled to the lower end of the connecting pipe 106 and extends downward, and the lower end of the gas-liquid introduction pipe 104 reaches a lower portion of the gas-liquid separation tank 100. A liquid discharge outlet 100a, communicating with a drain pipe 108, is provided in the bottom of the gas-liquid separation tank 100. A gas discharge outlet 100b, communicating with an exhaust pipe 110, is provided in the side wall of the gas-liquid separation tank 100. This gas discharge outlet 100b is located above the lower end of the gas-liquid introduction pipe 104. The exhaust pipe 110 communicates with an exhaust damper (not shown).
A gas-liquid two-phase flow, recovered in the drain receiver 102, moves through the gas-liquid introduction pipe 104 and is introduced into the interior of the gas-liquid separation tank 100. A liquid, which has been separated from the gas-liquid two-phase flow and has accumulated on the bottom of the gas-liquid separation tank 100, is discharged through the liquid discharge outlet 100a and the drain pipe 108. A gas, which has been separated from the gas-liquid two-phase flow and has ascended to the upper portion of the gas-liquid separation tank 100, flows through the gas discharge outlet 100b into the exhaust pipe 110, and is discharged through the exhaust damper.
In order to prevent the gas-liquid two-phase flow in the gas-liquid introduction pipe 104 from flowing into the exhaust pipe 110, a tapered portion 104a is provided in the lower end surface of the gas-liquid introduction pipe 104 on the opposite side from the exhaust pipe 110 (the side not facing the exhaust pipe 110).
A waste liquid/waste gas treatment apparatus and method has been proposed which, in order to efficiently discharge a mist of polishing liquid generated during polishing, simultaneously takes a polishing liquid and a mist of polishing liquid into a drain receiver, and introduces the mixed fluid through a common discharge pipe into a gas-liquid separation means to separate the mixed fluid into a waste liquid and a waste gas and discharge them (see e.g., Japanese laid-open patent publication No. 10-123336). A gas-liquid separator has also been proposed which has a housing for storing a liquid discharged from a liquid discharge section of a gas-liquid separation tank, the housing being provided with a liquid discharge outlet and a gas discharge outlet (see e.g., Japanese laid-open patent publication No. 2008-38712 and Japanese laid-open patent publication No. 2008-38714). Further, a gas-liquid separator has been proposed which has a spiral plate installed in a tubular nozzle for introducing a gas-liquid mixture into a tank (see e.g., Japanese laid-open utility model publication No. 62-109709).
The gas-liquid separator shown in FIG. 1 has the advantage that its compact structure is suitable for its installation at a low position e.g., in a polishing apparatus. However, the gas-liquid two-phase flow flows freely downward in the gas-liquid introduction pipe 104 without any obstructions, and the downward flow hits the bottom of the gas-liquid separation tank 100 with high impact. Therefore, if a liquid to be treated contains a foamable material, considerable foaming of the liquid will occur during treatment of the gas-liquid two-phase flow, resulting in generation of a large amount of bubbles in the liquid that has accumulated on the bottom of the gas-liquid separation tank 100. When a large amount of bubbles is generated in the gas-liquid separation tank 100, it is possible that the bubbles (liquid) may reach the exhaust pipe 110, flow into the exhaust pipe 110, and leak through e.g., a flange provided on a bottom of the exhaust damper.
In particular, a polishing apparatus uses a polishing liquid containing a foamable additive such as a dispersant, i.e., a liquid (foamable liquid) which is likely to generate bubbles. Further, a large amount of treatment water and a gas, such as nitrogen gas, are used in spray cleaning of a substrate (i.e., an atomizer cleaning) after polishing. Therefore, a large amount of bubbles are likely to be generated in the gas-liquid separation tank 100.